Field of the Invention
The present disclosure relates to the technology of driving the display panel, more specifically, to a pixel driving circuit and a display panel.
Description of the Related Art
The traditional Active Matrix Organic Light Emitting Diode (“AM-OLED”, hereinafter) is generally composed of a switch transistor, a driving transistor and a storage capacitor, i.e., the pixel driving mode of 2T1C is adopted thereof. When the scanning line is effective, the switch transistor is switched on, the input data signal is stored in the storage capacitor, and the storage capacitor controls to switch on the driving transistor by the stored voltage signal, thereby the input data voltage signal can be transformed into the required current signal for light-emitting OLED to display the different gray levels. FIG. 1 shows the 2T1C pixel circuit of LTPS (low temperature poly-silicon) AM-OLED in the related art.
Presently, the excimer laser anneal (ELA) is adopted in the process of LTPS, the threshold voltage (VTH) of the transistor is not uniform in the space, thereby the threshold voltage (VTH) of etch transistor has large difference. However, in the low gray level image, the nonuniformity of the LTPS AM-OLED with 2T1C structure in a small scope of the same direction will reach up to 30% to 40%, and the difference between the adjacent transistors also reach up to 20%. Moreover, when the pixel power line of the LTPS transistor is comparatively long, the power supply of the pixel circuit will generate a comparatively large IR drop, thereby the serious nonuniformity of the gray level generated in the display of AM-OLED. In the low gray level image, IR Drop of the 2T1C circuit with the same structure in 1.0V causes the nonuniformity of brightness reaching up to more than 70%. Due to the above mentioned cause, the problem that the long-range and the short-range of the AM-OLED display are not uniform, that is, the nonuniformity of the threshold voltage (VTH) of transistor will not be compensated, and the influence of the nonuniformity to the AM-OLED display caused by power supply IR drop will not be eliminated.
A related art has disclosed a pixel circuit, comprising a light emitting diode, a driving transistor, a capacitor, and a switch unit. The driving transistor has a first source/drain coupled to one end of the light emitting diode. The capacitor is coupled between a gate of the driving transistor and the end of the light emitting diode. The switch unit couples the gate and a second source/drain of the driving transistor together, and couples the second source/drain of the driving transistor to a data line when a scan signal is asserted.
Another related art has disclosed a pixel driving circuit. A photo sensor is used in this driving circuit for sensing light from illumination devices to generate different induced currents. The different induced currents may form different driving currents to drive the illumination devices. Therefore, the illumination period of each illumination device is different but results in a same brightness after integration of each illumination device through a frame time.
Consequently, the related arts have not solved the problem that the nonuniformity of the threshold voltage (VTH) of transistor can not be compensated and the influence to the nonuniformity of the AM-OLED display caused by power supply IR drop can not be eliminated.